A team of FBI agents has been conducting interviews in recent weeks in the Dominican Republic and the United States, looking into allegations that Sen. Robert Menendez (D-N.J.) patronized prostitutes in the Caribbean nation, but has found no evidence to support the claim, according to two people familiar with the investigation.

One person said agents have asked about whether a Florida eye doctor — a close friend and major campaign donor to Menendez — provided the senator with prostitutes on vacations there. Another person said investigators are looking into allegations involving underage prostitutes and sex parties.

The two, who spoke on the condition of anonymity to discuss an active investigation, said FBI agents are following leads provided by an unknown tipster. In a series of e-mails with the FBI, the tipster alleged that the doctor, Salomon Melgen, had made prostitutes available to Menendez while he was staying at his friend’s resort home in the Dominican Republic. The tipster, in particular, mentioned young prostitutes and prostitution parties.

The FBI agents are also examining the role Menendez played in advocating for a port security contract in the Dominican Republic that would benefit Melgen, two people familiar with the case said. Menendez has urged U.S. officials to put pressure on the Dominican government to enforce the dormant contract, saying enhanced port security is important for interdicting drug trafficking. Melgen is an investor in the company holding the contract.

FBI spokesman Michael Leverock, of the bureau’s field office in Miami, declined to comment for this article.

The focus of the Menendez story has already shifted from these initial accusations to a Senate Ethics Committee investigation about possible influence peddling by Menendez. As The Atlantic Wire writes today: